The present invention pertains to a high purity Ru powder for manufacturing a sputtering target having a purity of 4N (99.99%) or higher and which is suitable in forming a capacitor electrode material of a semiconductor memory, a sputtering target obtained by sintering such high purity Ru powder, a thin film obtained by sputtering said target, and a manufacturing method of the foregoing high purity Ru powder.
Today, the use of Ru as an electrode material or the like of a semiconductor capacitor is rapidly expanding. This kind of electrode is generally formed by sputtering a Ru target.
In order to guarantee the operational performance as a reliable semiconductor, it is important to reduce as much as possible impurities in the foregoing materials formed after sputtering that are harmful to the semiconductor device.
In other words, it is desirable to reduce:
alkali metal elements such as Na and K;
radioactive elements such as U and Th; and
transition metal elements such as Fe, Ni, Co, Cr and Cu;
as much as possible, and realize a purity of 4N or higher; that is, 99.99% (weight) or higher.
The reason the foregoing impurities are harmful is that alkali metals such as Na and K move easily in the gate insulator and cause the MOS-LSI interfacial quality to deteriorate, radioactive elements such as U and Th cause a soft error of elements due to alpha ray emitted from such elements, and transition metal elements such as Fe, Ni, Co, Cr and Cu contained as impurities cause trouble at the interface bonding.
Among the above, the harmful effect of alkali metals such as Na and K is particularly pointed out. Contrarily, transition metal elements such as Fe, Ni, Co, Cr and Cu are not considered to be as harmful, and the existence thereof of a certain amount is tolerated.
When reviewing the composition of conventional Ru targets, disclosed is ruthenium wherein the content of respective alkali metal elements is less than 1 ppm, the content of respective alkali earth metal elements is less than 1 ppm, the content of respective transition metal elements is less than 1 ppm, the content of respective radioactive elements is less than 10 ppb, the content of carbon and gas component elements (oxygen, hydrogen, nitrogen, chlorine) is less than 500 ppm in total, purity of ruthenium excluding gas components is 99.995% or higher, and the content of Al and Si is respectively less than 1 ppm (for instance, refer to Patent Document 1). Further, disclosed is ruthenium wherein the content of the respective elements of carbon, oxygen and chlorine is 100 ppm or less, and the purity of ruthenium excluding gas components is 99.995% or higher (for instance, refer to Patent Document 2). Moreover, disclosed is ruthenium wherein iron elements content is 5 ppm or less, the content of alkali metal elements is 1 ppm, the content of radioactive elements is 0.01 ppm or less, and tungsten content is 1 ppm or less (for instance, refer to Patent Document 3). In addition, disclosed is a high purity ruthenium sputtering target having a purity of 99.999wt % or higher (for instance, refer to Patent Document 4). Further, disclosed is a high purity ruthenium sputtering target wherein the content of respective alkali metal elements is 0.1 wtppm or less, the content of respective alkali earth metal elements is 0.1 wtppm or less, the content of respective transition metal elements excluding platinum group elements is 0.1 wtppm or less, the content of respective radioactive isotopes is 1 wtppb or less, the content of gas component elements is 30 wtppm or less in total, and having a purity of 99.995wt % (for instance, refer to Patent Document 5). Moreover, disclosed is a high purity ruthenium powder wherein the content of respective alkali metals, alkali earth metals, aluminum, iron, nickel, and copper is 0.1 ppm or less (for instance, refer to Patent Document 6). In addition, disclosed is a ruthenium sputtering target wherein the content of Na, K, Ca and Mg is 5 ppm or less in total, the content of one type or more among Fe, Ni and Co is in the range of 0.5 to 50 ppm, the content of radioactive isotopes is 5 ppb or less, and having a purity of 99.999wt % or higher excluding Fe, Ni and Co (for instance, refer to Patent Document 7). Further, disclosed is a high purity ruthenium sputtering target having a purity of 99.999% or higher (for instance, refer to Patent Document 8).    [Patent Document 1] Japanese Patent Laid-Open Publication No. H11-50163    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2000-34563    [Patent Document 3] Japanese Patent Laid-Open Publication No. H11 -217633    [Patent Document 4] Japanese Patent Laid-Open Publication No. H9-41131    [Patent Document 5] Japanese Patent Laid-Open Publication No. 2002-105631    [Patent Document 6] Japanese Patent Laid-Open Publication No. H9-227966    [Patent Document 7] Japanese Patent Laid-Open Publication No. H8-199350    [Patent Document 8] Japanese Patent Laid-Open Publication No. H8-302462
When reviewing the foregoing Patent Documents, it could be said that they all disclose technology for reducing as much as possible the impurities in ruthenium considered to be harmful and realizing even higher purity in order to guarantee the operational performance as a semiconductor.
Nevertheless, as a sputtering target to be used in forming a capacitor electrode material of a semiconductor memory, characteristics where the generation of particles during deposition is minimal and the film thickness distribution is uniform are required, but there is a problem in that such characteristics are insufficient under existing circumstances.